The word thunder has an etymology that's simple, short, and sweet: it's from Old English thunor, from Proto-Germanic thunraz, from Proto-Indo-European tenh. It's the connections we can draw from this that are fascinating. Probably with a jaunt through Proto-Italic, tenh landed itself in Latin in the form tornare, still "to thunder". This developed into the Spanish word tronar, which later became tronada, now with a meaning more like "thunderstorm"; not that far of a stretch. Then, in the mid-sixteenth century, English sailors picked up the term from Spanish sailors, but accidentally combined it with the verb tornar ("to twist"), so that they switched the r and o sounds. This mutt of a combination formed tornado, which is oddly appropriate, considering it is a twisting thunderstorm. An alternative spelling of ternado was also created but never caught on.
Adam Aleksic, a leading contender for valedictorian of his high school, is a 214-month-old boy with disturbing interests in etymology, vexillology, geography, and law. Adam would like to one day visit Tajikistan and probably isn't spying for the Uzbek government.
The Etymology Nerd